I am not the least bit surprised that a gang of these thugs would slice someones head off while they were alive to experience it.
Remember when a couple of these fellas flew 767s loaded with innocent passengers, women and children, into skyscrapers.
Just tag em and bag em. in the short term thats all that can be done. Long term is to bring these barbarians, by love, candy, force...whatever, into the civilized world, whether they like it or not, the jig is up.
Good news is we have the capability to zap these bastards. Maybe not on schedule but zap them we are. Everyday SF guys and other specialized forces are putting these animals into petre dishes for DNA analysis. Fight the good fight and if you cant seem to figure out who the good guys are then maybe you need to be petre dished.